You can find the library on GITHUB. Place all files in a newly created folder named "AD7887" in the library folder of your Arduino installation. Usually the "libraries" folder in your sketch folder. If you install the library correctly it will appear under the SENSOR section in the Arduino IDE library manager.

Here you can see some time diagrams:

I've used the SPI decoding function of my Rigol MSO2072A - this works pretty good!

D0 == /ChipSelect

D1 == SerialClock

D2 == Data from AD7887

D3 == Data to AD7887

As you can see, the speed is not so good. The library is using the standard Arduino implemenation of digitalWrite() command - they are horrible slow ...